I cannot edit the super flat preset, nor can I copy it.
It can also be earlier versions, but I'm running out of time to test that.

What I expected to happen:
Same behaviour as 1.12.2, I can edit for example the blocks used in the preset.

What actually happened:
I can click in the box, but I can't remove letters or type something. I also can't copy it, or select it all.

Steps to reproduce:

1. Create a new world
2. Click more world options
3. Select World Type "Superflat
4. Click "Customise"
5. Click "Presets"
6. Attempt to edit the box with your preset, or attempt to copy it.
7. Notice that it won't work.

If you don't know what box with preset I'm talking about, I added a screenshot of that box.